The present invention relates to a valve and an actuator for a valve. In particular, the present invention relates to a valve having an actuator responsive to rotational input for moving a first valve part axially between open and closed positions relative to a second valve part.
Many industrial valves have a valve member, such as a valve stem, that is movable relative to a valve seat between an open position spaced apart from the seat, enabling fluid flow through the valve, and a closed position in engagement with the valve seat. The movable valve member is often held in engagement with the valve seat by a spring. Over time, the valve member and/or the valve seat may wear, or under continued loading experience material creep, especially if made from plastic. If the valve member is not able to move farther toward the valve seat to compensate for such wear or creep, the valve may not close completely in some circumstances.
Some valves have a cam mechanism for opening and closing the valve. If the cam mechanism is interposed between the closing spring and the movable valve member, the cam mechanism may undesirably limit compensating movement of the valve member. In addition, the parts of the cam mechanism, themselves, if made from plastic, may be subject to material creep and/or deformation if subjected to the force of the closing spring for an extended period of time.